Re: fspacectl(2): result of rmsr.r_offset for a success and non-partial operation

On 2021/8/20 11:23 PM, Ka Ho Ng wrote:
> There were some recent discussion in https://reviews.freebsd.org/D31604
> around the returned value of rmsr.r_offset. For a complete and
> successful operation, rmsr.r_len is set to 0. Regarding rmsr.r_offset,
> the bottom line is to have rmsr.r_offset being no greater than current
> file size in case rmsr.r_offset is greater than file size, while leaving
> rmsr.r_offset to be within EOF in case rqsr.r_offset is not beyond EOF.
> 
> With the current approach, rmsr.r_offset is loosely defined as file
> system is free to set it to some value as long as it is neither smaller
> than rqsr.r_offset (in case rqsr.r_offset is within EOF), or beyond EOF
> (in case rqsr.r_offset is beyond EOF). Do you think it is a good idea to
> make it stricter in case the call succeeds and rmsr.r_len == 0 (i.e. a
> complete operation)? If that is the case, what if we set rmsr.r_offset
> to be rqsr.r_offset + rqsr.r_len?
> 
> Ka Ho
> 

My another approach is to explicitly document that for a complete and
successful operation (i.e. rmsr.r_len == 0) callers need not to consider
the exact value of rmsr.r_offset, except if the operation range is not
complete outside of EOF, rmsr.r_offset is not going to be outside of EOF
either.

Ka Ho